Darunavir is a potent HIV protease inhibitor, which is chemically known as [(1S,2R)-3-[[(4-Aminophenyl)sulfonyl](2-methylpropyl)amino]-2-hydroxy-1-(phenylmethyl) propyl]carbamic acid, (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl ester, represented by Formula I.
Darunavir is a new generation of non-peptide protease inhibitor (PI). It is exceeding potent and has shown impressive broad-spectrum activity against highly cross-resistant HIV mutants. Darunavir is being marketed under the brand name Prezista® as an oral tablet and oral suspension in the form of monoethanolate solvate.
Prezista® must be co-administered with Ritonavir to exert its therapeutic effect. Failure to correctly co-administer Prezista® with Ritonavir will result in plasma levels of Darunavir that will be insufficient to achieve the desired antiviral effect and will alter some drug interactions.
Darunavir is generically disclosed in U.S. Pat. No. 5,843,946, specifically disclosed in U.S. Pat. No. 6,248,775. However, in these patents, there is no specific example for preparing Darunavir.
U.S. Pat. No. 6,248,775 discloses a process for preparing 2R-hydroxy-3-[[4-aminophenyl) sulfonyl](2-methylpropyl)amino]-1S-(phenylmethyl)propylamine, which is referred as Diamino alcohol a compound of Formula II,
a key intermediate in the preparation of Darunavir.
The process is as shown below:

This process involves the use of benzyloxycarbonyl (Cbz) protection, which needs to be deprotected by catalytic hydrogenation using palladium on carbon catalyst and hence the process is not industrially and commercially cost effective.
Bioorganic Medicinal Chemistry Letters 8, 1998, 687-690, discloses a process to prepare Darunavir as well as Diamino alcohol a compound of Formula II, which is as shown below:

This process involves the use of highly hazardous azide intermediate and hence not suitable for commercial production.
U.S. Pat. No. 7,772,411 B2 discloses a process to prepare Diamino alcohol a compound of Formula II, which is as shown below:

The present inventors has repeated the above process and found the following disadvantages:
1. Diamino alcohol preparation was carried out in one pot and the purity of obtained product was found to low.
2. Unwanted reactions observed during the formation of nitro compound (A), which is due to the existence of isobutylamine after the completion of epoxide condensation with isobutylamine. The unwanted isobutylamine reacts with p-nitrobenzenesulfonyl chloride to give the N-isobutyl 4-nitrobenzenesulfonamide impurity of Formula XI.

Further, this N-isobutyl 4-nitrobenzenesulfonamide impurity of Formula XI, participate in the next reactions to give corresponding impurities.
3. Sulfonamide reaction is carried out at higher temperature i.e., 82-88° C., wherein the product undergoes degradation and observed that the reaction mass becomes very thick, which is very difficult to stir/mix.
4. The isolation of Diamino alcohol is tedious, wherein it involves pH adjustment, water content adjustment and concentration.
In view of the above and to overcome the prior-art problems the present inventors have now developed an improved process for the preparation of Diamino alcohol having high purity and yield, which is further converted to Darunavir or its pharmaceutically acceptable salts, solvates thereof, having high yield and purity.
U.S. Pat. No. 7,700,645 discloses several pseudopolymorphs of Darunavir, including the ethanolate, hydrate, methanolate, acetonate, dichloromethanoate, ethyl acetate, 1-methoxy-2-propanolate, anisolate, tetrahydrofuranate, isopropanolate and mesylate solvates; US 2011/0313035 discloses Darunavir C5-8 alcohol solvate, wherein C5-8 alcohol solvate is selected from 2-methyl-2-butanol and n-pentanol; US 2012/0035142 discloses Darunavir dimethylsulfoxide solvate, Tetrahydrofuran solvate.
New polymorphic forms and solvates of a pharmaceutically useful compound or salts thereof can also provide an opportunity to improve the performance characteristics of a pharmaceutical product and new solvates of Darunavir that may have advantageous physico-chemical and biokinetic properties such as suitable solubility in neutral, acidic or alkaline water medium, solubility in technologically important organic solvents, water/lipid partition coefficient, electrochargeability, thermal stability, water and oxygen inertness, hygroscopicity, crystal shape, particle size and surface, dissolution profile, compatibility with excipients and combined active ingredients or special properties for final dosage form design.
Journal of Organic Chemistry 2004, 69, 7822-7829 discloses a process for preparing amorphous Darunavir, by purifying Darunavir by column chromatography.
European Journal of Pharmaceutical Sciences 2009, 38, 489-497 discloses processes for the preparation of amorphous Darunavir.                by melting Darunavir hydrate or ethanolate on a Kofler hot bar and cooling        by dissolving Darunavir ethanolate in MDC and spray drying        
The prior-art processes involve the use of chromatographic and spray drying techniques. Hence, there is a need in the art to develop an improved process for the preparation of amorphous Darunavir.
The present inventors have found that Darunavir ethanolate is hygroscopic and converts to Darunavir hydrate at moderate or high relative humidity at 25° C. Further, the isolation of Darunavir ethanolate involves special precautions during isolation, drying and powder processing, which is onerous during the large scale manufacturing of Darunavir ethanolate.
In view of the above, the present inventors have now developed novel solvates of Darunavir, which are stable solvates and does not require laborious isolation. Further, the present inventors developed an improved process for the preparation of amorphous Darunavir from Darunavir or its solvates thereof.